int
umain() {
    asm volatile(
            ".global sys_yield\n\t"
            ".bss\n\t"
            ".comm a, 1\n\t"
            ".comm sys_yield, 8\n\t"
            //".comm cprintf, 8\n\t"

            ".text\n\t"
            // ".set global_alias, cprintf"
            :
            :
            :);
    return 0;
}